A new triterpenoid glycoside, 3b-O-a-L-arabinopyranosyl rotundic acid, named here mateside (4), and the known triterpenes ursolic acid (1), acetylursolic acid (2), 23-hydroxyursolic acid (3), the saponins ziyu-glycoside I (5) and ilexoside II (6), were isolated from fruits of Ilex paraguariensis. Their structures were established on the basis of 1D and 2D NMR spectroscopic methods. The threshold bitterness values for mateside and ilexoside II were also determined and compared with saponins obtained from leaves of I. paraguariensis and other Ilex species. The high bitterness of Ilexoside II, one of the main saponins found the fruits, but not in the leaves of I. paraguariensis, suggests that the utilization of the fruits in the Maté production can produce a strong taste variation and unknown physiological effects.